[es6] Self-assignment in a default parameter initializer should throw

test/message/default-parameter-tdz.js

Index: test/message/default-parameter-tdz.js
diff --git a/test/message/arrow-two-rest-params.js b/test/message/default-parameter-tdz.js
similarity index 73%
copy from test/message/arrow-two-rest-params.js
copy to test/message/default-parameter-tdz.js
index 44eb47e5f626ba0d6b3a0474d8c10548ec304d6f..82fa87107f87930bff51389b53f6c9def52a0d53 100644
--- a/test/message/arrow-two-rest-params.js
+++ b/test/message/default-parameter-tdz.js
@@ -2,6 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Flags: --harmony-rest-parameters
+// Flags: --harmony-default-parameters
 
-(w, ...x, ...y) => 10
+(function(a=a) { })();